1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device that can form the metal film having high coating characteristics and adhesion on the semiconductor substrate at low costs.
2. Background Art
When electrodes other than an ohmic electrode are formed on a semiconductor substrate, generally, two layers or more metal films are often formed using vapor deposition, sputtering or the like. For the upper layer, a material having high electric conductivity, whose surface is hard to be oxidized, such as Au, is used. In place of Au, Ag, Cu or the like may be used. The lower layer is a barrier layer that prevents the diffusion of Au into the semiconductor substrate. As the barrier layer, Ti, TiN, TaN, Pt or the like is often used. Furthermore, in order to secure required current, these layers may be subjected to Au electrolytic plating as power supply layers. In place of Au electrolytic plating, Ag or Cu having high conductivities may also be used.
As the characteristics of the electrode, in addition to electrical characteristics, such as low electric resistance and electro-migration suppression, a sufficient adhesion is required for preventing peel-off during die bonding or wire bonding. Therefore, as the metal for the electrode contacting the surface of the semiconductor, a metal having a high adhesion to the semiconductor is used. For example, Ti or Pt is used for GaAs.
In addition, when a penetrating electrode that electrically connects the top surface side to the back surface side of the substrate is formed in the via hole that penetrates through the semiconductor substrate, the inner wall of the via hole must be sufficiently coated with a metal film. When the metal film is formed using vapor deposition or sputtering, the metal film on the sidewall of the via hole becomes thinner than the metal film on other portions. Therefore, the efficiency of forming the metal film on the sidewall of the via hole is elevated using inverse sputtering or planetary vapor deposition.